1. Field of Technology
The present invention relates to a high-luminance planar illumination device using a laser light source and used in a non-emissive display device such as a liquid crystal television and a liquid crystal display device using the same.
2. Description of the Background Art
A liquid crystal display device adopts a method for displaying an image by controlling a transmission amount of light irradiated from behind utilizing an electrooptic effect by the orientation of liquid crystal molecules and generally requires a planar illumination device called a backlight unit formed by fluorescent display tubes. In recent years, screens of such liquid crystal display devices have become larger and display devices for televisions of 50 inches and larger have been put to practical use. However, since power consumption has also been increased as screens have become larger, technological development for realizing lower power consumption is hoped for and it is strongly demanded to thin display devices in order to maximally reduce indoor spaces taken up by display devices.
In order to deal with lower power consumption out of such demands, it has been studied to use light-emitting diodes and laser light sources with good emission efficiency, and planar illumination devices using light emitting diodes as light sources have been already put to practical use.
It has been, for example, proposed that an optical fiber is connected with a side surface of a light guide plate called a light pipe and having a scattering center for scattering light, laser light from a laser light source is guided via this optical fiber to be incident on the light guide plate and scattered by the scattering center to emit output light from a principal surface of the light guide plate, whereby this construction is caused to function as a backlight unit (see, for example, patent literature 1). The laser light source can be arranged at an optimal position in terms of heat radiation by doing so, whereby it is tried to realize a lower power consuming and thin planar illumination device.
It has been also proposed that a plurality of slits are formed at one end of a transparent sheet, pieces between these slits are placed one over another to form a strip-shaped light guiding portion and light from a LED light source is incident on this strip-shaped light guiding portion to guide the light to the transparent sheet and output light is emitted from a surface of this light guiding sheet by scattering the light propagating in the sheet (see, for example, patent literature 2). By doing so, it is tried to realize a lightweight sheet-shaped planar illumination device with a uniform illuminance distribution.
However, in the prior arts described above, it is proposed to realize thinner planar illumination devices, but only insufficient numbers of the optical fibers and the strip-shaped light guiding portion are connected with the light guide plates and connecting structures with the light guide plates are not elaborated. Therefore, there is a problem of being unable to realize sufficiently accurate uniformity of output light from one principal surface of the light guide plate.    Patent Literature 1:
Japanese Unexamined Patent Publication No. 2007-42640    Patent Literature 2:
Japanese Unexamined Patent Publication No. 2005-340160